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Seismic Waves
Seismic Waves (notes)
• Wave shape: Transverse and longitudinal
• Wave type: Mechanical
• Medium: The Earth
• Structure:
• Composed of two parts: a longitudinal P-wave and a transverse S-wave.
The Fault In Our Earth (notes)
• Earthquakes are produced by the Earth
moving along faults
• Faults are areas where two volumes of
rock have been shifted relative to each
other
• Faults are produced by the movement
of the tectonic plates on the Earth’s
surface
Piqiang Fault, China
Wasatch Fault (not notes)
• We have a fault line running through
our area called the Wasatch Fault
• Because we are close to a lake,
another concern is something called
“liquefaction”, which is when loose,
sandy soil behaves like a liquid when
shaken
• After class if interested I have a map
up front of Davis County’s fault lines
Faults =/= Plate Boundaries (not notes)
• A plate boundary is where two major tectonic plates on the Earth’s
surface meet
• Faults are only minor “stretches” or “slips” that are a result of these
larger plates moving
P-Waves (notes)
• P-wave stands for “primary wave” because it is faster and reaches us
first
• P-waves are longitudinal waves
S-Waves (notes)
• S-wave stands for “secondary wave” because it is slower and reaches
us after the P-wave
• S-waves are transverse waves
Locating Earthquakes (not notes)
• Because P-waves and S-waves travel at different speeds, we can use
the difference in time to estimate the distance of an earthquake
Close near source
P-Wave
S-Wave
Separated far from source
The further away an earthquake is the more separation
between the arrival time of the P-waves and S-waves.
Think of it like timing the distance of lightning by counting
the difference between the arrival of light and sound.